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From: Greg Kroah-Hartman on 5 Aug 2010 18:40
From: Feng Tang <feng.tang(a)intel.com>

A general problem for uart rx dma channel is you never know when
and how much data will be received, so usually preset it a DMA
descriptor with a big size, and rely on DMA RX timeout IRQ to
know there is some data in rx channel.

For a RX data size of multiple of MOTSR, there will be no timeout
IRQ issued, thus OS will never be notified about that.

This is a work around for that, current timer frequency is 5 times
per second, it should vary according to the baud rate

When future silicon version fix the problem, this workaround need
be removed

Signed-off-by: Feng Tang <feng.tang(a)intel.com>
Signed-off-by: Alan Cox <alan(a)linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>
---
drivers/serial/mfd.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++---
1 files changed, 47 insertions(+), 3 deletions(-)

diff --git a/drivers/serial/mfd.c b/drivers/serial/mfd.c
index 300dcb13..ed2bf6b 100644
--- a/drivers/serial/mfd.c
+++ b/drivers/serial/mfd.c
@@ -64,6 +64,8 @@
#define mfd_readl(obj, offset) readl(obj->reg + offset)
#define mfd_writel(obj, offset, val) writel(val, obj->reg + offset)

+#define HSU_DMA_TIMEOUT_CHECK_FREQ (HZ/10)
+
struct hsu_dma_buffer {
u8 *buf;
dma_addr_t dma_addr;
@@ -75,7 +77,8 @@ struct hsu_dma_chan {
u32 id;
u32 dirt; /* to or from device */
struct uart_hsu_port *uport;
- void __iomem *reg;
+ void __iomem *reg;
+ struct timer_list rx_timer; /* only needed by RX channel */
};

struct uart_hsu_port {
@@ -377,6 +380,8 @@ void hsu_dma_start_rx_chan(struct hsu_dma_chan *rxc, struct hsu_dma_buffer *dbuf
| (0x1 << 24) /* timeout bit, see HSU Errata 1 */
);
chan_writel(rxc, HSU_CH_CR, 0x3);
+
+ mod_timer(&rxc->rx_timer, jiffies + HSU_DMA_TIMEOUT_CHECK_FREQ);
}

/* Protected by spin_lock_irqsave(port->lock) */
@@ -437,8 +442,13 @@ void hsu_dma_rx(struct uart_hsu_port *up, u32 int_sts)
/* We can use 2 ways to calc the actual transfer len */
count = chan_readl(chan, HSU_CH_D0SAR) - dbuf->dma_addr;

- if (!count)
+ if (!count) {
+ /* restart the channel before we leave */
+ chan_writel(chan, HSU_CH_CR, 0x3);
return;
+ }
+
+ del_timer(&chan->rx_timer);

dma_sync_single_for_cpu(port->dev, dbuf->dma_addr,
dbuf->dma_size, DMA_FROM_DEVICE);
@@ -463,9 +473,12 @@ void hsu_dma_rx(struct uart_hsu_port *up, u32 int_sts)
| (0x1 << 16)
| (0x1 << 24) /* timeout bit, see HSU Errata 1 */
);
+ tty_flip_buffer_push(tty);
+
chan_writel(chan, HSU_CH_CR, 0x3);
+ chan->rx_timer.expires = jiffies + HSU_DMA_TIMEOUT_CHECK_FREQ;
+ add_timer(&chan->rx_timer);

- tty_flip_buffer_push(tty);
}

static void serial_hsu_stop_rx(struct uart_port *port)
@@ -893,6 +906,8 @@ static void serial_hsu_shutdown(struct uart_port *port)
container_of(port, struct uart_hsu_port, port);
unsigned long flags;

+ del_timer_sync(&up->rxc->rx_timer);
+
/* Disable interrupts from this port */
up->ier = 0;
serial_out(up, UART_IER, 0);
@@ -1348,6 +1363,28 @@ err_disable:
return ret;
}

+static void hsu_dma_rx_timeout(unsigned long data)
+{
+ struct hsu_dma_chan *chan = (void *)data;
+ struct uart_hsu_port *up = chan->uport;
+ struct hsu_dma_buffer *dbuf = &up->rxbuf;
+ int count = 0;
+ unsigned long flags;
+
+ spin_lock_irqsave(&up->port.lock, flags);
+
+ count = chan_readl(chan, HSU_CH_D0SAR) - dbuf->dma_addr;
+
+ if (!count) {
+ mod_timer(&chan->rx_timer, jiffies + HSU_DMA_TIMEOUT_CHECK_FREQ);
+ goto exit;
+ }
+
+ hsu_dma_rx(up, 0);
+exit:
+ spin_unlock_irqrestore(&up->port.lock, flags);
+}
+
static void hsu_global_init(void)
{
struct hsu_port *hsu;
@@ -1409,6 +1446,13 @@ static void hsu_global_init(void)
dchan->uport = &hsu->port[i/2];
dchan->reg = hsu->reg + HSU_DMA_CHANS_REG_OFFSET +
i * HSU_DMA_CHANS_REG_LENGTH;
+
+ /* Work around for RX */
+ if (dchan->dirt == DMA_FROM_DEVICE) {
+ init_timer(&dchan->rx_timer);
+ dchan->rx_timer.function = hsu_dma_rx_timeout;
+ dchan->rx_timer.data = (unsigned long)dchan;
+ }
dchan++;
}

--
1.7.2

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Prev: [PATCH 55/67] serial: mcf: don't take spinlocks in already protected functions
Next: [PATCH 17/28] sysfs: Fix one more signature discrepancy between sysfs implementation and docs.